Cornelia Huck
2014-Nov-17 09:44 UTC
[PATCH V3 1/2] virtio: introduce methods of sanitizing device features
On Mon, 17 Nov 2014 11:37:01 +0200 "Michael S. Tsirkin" <mst at redhat.com> wrote:> On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote: > > Buggy host may advertised buggy host features (a usual case is that host > > advertise a feature whose dependencies were missed). In this case, driver > > should detect and disable the buggy features by itself. > > > > This patch introduces driver specific sanitize_features() method which is > > called just before features finalizing to detect and disable buggy features > > advertised by host. > > > > Virtio-net will be the first user. > > > > Cc: Rusty Russell <rusty at rustcorp.com.au> > > Cc: Michael S. Tsirkin <mst at redhat.com> > > Cc: Cornelia Huck <cornelia.huck at de.ibm.com> > > Cc: Wanlong Gao <gaowanlong at cn.fujitsu.com> > > Signed-off-by: Jason Wang <jasowang at redhat.com> > > Hmm this conflicts with virtio 1.0 work: we drop > features as bitmap there.But that's an implementation detail, no? We'll still need a way for the driver to sanitize features, and I think this interface works just fine.
Michael S. Tsirkin
2014-Nov-17 10:11 UTC
[PATCH V3 1/2] virtio: introduce methods of sanitizing device features
On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote:> On Mon, 17 Nov 2014 11:37:01 +0200 > "Michael S. Tsirkin" <mst at redhat.com> wrote: > > > On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote: > > > Buggy host may advertised buggy host features (a usual case is that host > > > advertise a feature whose dependencies were missed). In this case, driver > > > should detect and disable the buggy features by itself. > > > > > > This patch introduces driver specific sanitize_features() method which is > > > called just before features finalizing to detect and disable buggy features > > > advertised by host. > > > > > > Virtio-net will be the first user. > > > > > > Cc: Rusty Russell <rusty at rustcorp.com.au> > > > Cc: Michael S. Tsirkin <mst at redhat.com> > > > Cc: Cornelia Huck <cornelia.huck at de.ibm.com> > > > Cc: Wanlong Gao <gaowanlong at cn.fujitsu.com> > > > Signed-off-by: Jason Wang <jasowang at redhat.com> > > > > Hmm this conflicts with virtio 1.0 work: we drop > > features as bitmap there. > > But that's an implementation detail, no? We'll still need a way for the > driver to sanitize features, and I think this interface works just fine.Now that you mention it, I don't think we do. The spec is quite explicit that devices must not expose invalid combinations of features. Admittedly, BUG_ON isn't very friendly to hypervisors. But e.g. failing probe seems better than trying to work around hypervisor bugs - otherwise we'll be stuck maintaining compatibility with hypervisors forever. -- MST
Cornelia Huck
2014-Nov-17 10:20 UTC
[PATCH V3 1/2] virtio: introduce methods of sanitizing device features
On Mon, 17 Nov 2014 12:11:39 +0200 "Michael S. Tsirkin" <mst at redhat.com> wrote:> On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote: > > On Mon, 17 Nov 2014 11:37:01 +0200 > > "Michael S. Tsirkin" <mst at redhat.com> wrote: > > > > > On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote: > > > > Buggy host may advertised buggy host features (a usual case is that host > > > > advertise a feature whose dependencies were missed). In this case, driver > > > > should detect and disable the buggy features by itself. > > > > > > > > This patch introduces driver specific sanitize_features() method which is > > > > called just before features finalizing to detect and disable buggy features > > > > advertised by host. > > > > > > > > Virtio-net will be the first user. > > > > > > > > Cc: Rusty Russell <rusty at rustcorp.com.au> > > > > Cc: Michael S. Tsirkin <mst at redhat.com> > > > > Cc: Cornelia Huck <cornelia.huck at de.ibm.com> > > > > Cc: Wanlong Gao <gaowanlong at cn.fujitsu.com> > > > > Signed-off-by: Jason Wang <jasowang at redhat.com> > > > > > > Hmm this conflicts with virtio 1.0 work: we drop > > > features as bitmap there. > > > > But that's an implementation detail, no? We'll still need a way for the > > driver to sanitize features, and I think this interface works just fine. > > Now that you mention it, I don't think we do. > > The spec is quite explicit that devices must not expose invalid > combinations of features.Unfortunately, this does not ensure that there won't be buggy hypervisors out there, just as there's buggy hardware floating around.> > Admittedly, BUG_ON isn't very friendly to hypervisors. > > But e.g. failing probe seems better than trying to work around > hypervisor bugs - otherwise we'll be stuck maintaining compatibility > with hypervisors forever.Good point. Failing probe is still much better than hitting BUG_ONs. We'll still need a driver callback, though, that can return an error on bogus feature bit combinations.
Jason Wang
2014-Nov-18 03:23 UTC
[PATCH V3 1/2] virtio: introduce methods of sanitizing device features
On 11/17/2014 06:11 PM, Michael S. Tsirkin wrote:> On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote: >> On Mon, 17 Nov 2014 11:37:01 +0200 >> "Michael S. Tsirkin" <mst at redhat.com> wrote: >> >>> On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote: >>>> Buggy host may advertised buggy host features (a usual case is that host >>>> advertise a feature whose dependencies were missed). In this case, driver >>>> should detect and disable the buggy features by itself. >>>> >>>> This patch introduces driver specific sanitize_features() method which is >>>> called just before features finalizing to detect and disable buggy features >>>> advertised by host. >>>> >>>> Virtio-net will be the first user. >>>> >>>> Cc: Rusty Russell <rusty at rustcorp.com.au> >>>> Cc: Michael S. Tsirkin <mst at redhat.com> >>>> Cc: Cornelia Huck <cornelia.huck at de.ibm.com> >>>> Cc: Wanlong Gao <gaowanlong at cn.fujitsu.com> >>>> Signed-off-by: Jason Wang <jasowang at redhat.com> >>> Hmm this conflicts with virtio 1.0 work: we drop >>> features as bitmap there. >> But that's an implementation detail, no? We'll still need a way for the >> driver to sanitize features, and I think this interface works just fine. > Now that you mention it, I don't think we do. > > The spec is quite explicit that devices must not expose invalid > combinations of features. > > Admittedly, BUG_ON isn't very friendly to hypervisors. > > But e.g. failing probe seems better than trying to work around > hypervisor bugs - otherwise we'll be stuck maintaining compatibility > with hypervisors forever. >I'm ok with failing the probe. But it won't cost big effort to workaround only features dependencies issue. I don't see how this block any further features implementation. Looking at virtio-net, it also depends on network core to fix NETIF_F_* dependencies. There seems no way to get rid of maintaining compatibility, e.g the workarounds for the buggy hypervisor without VIRTIO_F_ANY_LAYOUT support.
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